I booked another trip to Cambodia today and thought I would give the e-visa a try. Usually I just get a tourist or business visa at the airport or border on arrival. The cost is $25 for a tourist visa so $5 more than at the airport on arrival. One benefit is you don't have to wait while your visa is processed and you can walk straight to the Immigration points. You also save a valuable page in your passport and you don't have to go and get passport photos taken.
Cambodia Visa, Apply Cambodia Visa Online, Cambodia e-Visa - Official Site
Applying for it is easy enough, just make sure you have your travel and arrival details on hand to complete the application.
You'll need a digital photo of yourself to send with the application.
Payment is unfortunately through Paypal only I believe but that wasn't too much of a problem.
The process is surprisingly efficient and quick. My visa was processed within minutes and moments later I received an email with the picture of the visa for printout.
On arrival in Cambo you present the printout, your passport and the completed Arrival card at the Immigration desk and when you leave you present another copy with your passport and departure card.
Simple enough. I would also recommend it to those travelling overland, although it is not accepted at all border crossings so check first. It may mean you don't have to deal with any touts.